Fibrous webs for absorbing a wide variety of liquids are widely used for a variety of purposes. Fibrous webs are made from a plurality of individual fibers which are bonded to one another to provide the web some degree of structural integrity, so that it can retain its shape during manufacture, handling, and/or use. Void volume within the web provides capacity for absorbing and retaining liquids. One of the disadvantages of fibrous webs is that individual fibers incorporated into the web, especially at the surface of the web, can become loose and separate from the web. This is referred to as linting.
In many applications, the web is enclosed within a confined volume by one or more liquid permeable sheets. For example, diapers have an absorbent web enclosed within a nonpermeable backsheet layer and a liquid permeable topsheet layer. The topsheet and backsheets contain any lint that may separate from the web. The fibers of some webs are bonded to one another to reduce linting.
One method of bonding the fibers is to thermally bond them together with polymeric bonding materials, such as but not limited to polypropylene, polyethylene, and other polyolefins. Other bonding technologies frequently used include adhesive agents and polymeric resins. Still other webs are made from polymeric fibers which, when heated to a high enough temperature, become partially molten or flowable. When the web is cooled, those synthetic fibers in sufficient proximity to one another to cause the molten polymer for adjacent polymers to contact one another become thermally bonded as temperature falls below the melting or glass transition point of the polymer. A disadvantage of these types of bonding methods is that the bonding agents added to the web can adversely affect absorbency and softness of the web. Another disadvantage of thermally bonded webs is that they do not retain structural integrity at temperatures above the melting temperature or glass transition temperature of the polymer used to thermally bond the fibers. Thus, webs relying upon thermal bonding to control lint would not be useful for applications in which they are exposed to high temperatures, such as when used as heat insulators, for example in a pot holder or for industrial or construction purposes. Another application wherein the webs may be exposed to high temperatures is absorption of oils from food during cooking. If stable at temperature, such webs may be contacted with foods during cooking, or even intermixed in the food, to absorb fats and oils. Typical temperatures experience during stove-top cooking, for example, can range from about 120 C to about 175 C.
Another method of bonding fibers together is known as entangling. Entangling the fibers entails mechanical interlocking of the fibers to one another. One commonly known method for entanglement is needling (also referred to as felting), wherein a barbed needle is inserted into the web and then removed, causing entanglement at the point of insertion. Another method of entanglement is hydroentanglement, wherein narrow jets of water are directed at the web to cause the fibers to become entangled. Although needling can introduce significant improvements in structural integrity to the web, such webs having high levels of absorbency typically suffer from relatively high levels of lint. When entanglement is increased sufficiently to reduce lint, the web typically suffers from reduced absorbency. It is also known to thermally bond synthetic fibers of non-woven webs by calendar rolls or other compressive means, such as is in the manufacture of inexpensive non-woven fabrics used to make disposable clothing, e.g., surgical gowns. These types of materials are generally thin and would have poor absorbency.
British Patent 1,124,482, granted Sep. 21, 1965, Ludlow Corporation, discloses a process for manufacturing polyolefin fiber-containing non-woven fabric in which one surface is heated to fuse the thermoplastic fibers. A thermo-responsive resin then added to the web melted by hot air. This product would not have good high temperature stability once exposed to a high enough temperature to melt the thermo-responsive resin.
U.S. Pat. No. 4,810,315, issued Mar. 7, 1989, A. A. Zufang and R. A. M. J. Fabrie, discloses a method for making a web of plastic material having a base layer of plastic fibers which are heat treated at one surface. A second layer of plastic material, having a higher plasticizing temperature than the base layer, is then laminated to the heated surface of the base layer. The resulting web is said to retain porosity. However the lamination process described therein would not reduce Tinting of the resulting product, particularly at the exterior surfaces of the product.
It is an object of this invention to provide fibrous webs that are both absorbent and have low levels lint.
It is a further object of this invention to provide fibrous webs that are absorbent and retain structural integrity upon exposure to relatively high temperatures during use.
It is yet another object of this invention to provide fibrous webs that are absorbent, have low levels of lint, and retain structural integrity upon exposure to relatively high temperatures during use.
It is still another object of this invention to provide a method for making fibrous webs that meet the above objects.
It is yet another object of this invention to provide methods of using such fibrous webs.
These and other object and benefits of the invention may become apparent to those of ordinary skill in the art may be achieved as a result of the invention as described in the specification and defined in the claims which follow.
All percentages are by weight of the total composition or product unless otherwise indicated. All averages are weight averages unless otherwise indicated. All products or processes that comprise one or more elements disclosed or claimed herein may alternately consist of or consist essentially of any elements disclosed or claimed herein.